A communication packet can also be a binlog event sent from the master to the slave.
To be sent by master dump and accepted by slave io thread both have to have
the value of max_allowed_packet bigger than one that client connection had.

In the patch there is the MAX possible replicatio header size estimation for events
in binlog that embedded user query. Only these events of query_log_event type, i.e
just plain queries, require attention.